Defense Secretary Jim Mattis has asked the White House to lift Obama-era restrictions on U.S. military support for Persian Gulf states engaged in a protracted civil war against Iranian-backed Houthi rebels in Yemen, according to senior Trump administration officials.

In a memo this month to national security adviser H.R. ­McMaster, Mattis said that “limited support” for Yemen operations being conducted by Saudi Arabia and the United Arab Emirates — including a planned Emirati offensive to retake a key Red Sea port — would help combat a “common threat.”

Approval of the request would mark a significant policy shift. U.S. military activity in Yemen until now has been confined mainly to counterterrorism operations against al-Qaeda’s affiliate there, with limited indirect backing for gulf state efforts in a two-year-old war that has yielded significant civilian casualties.

It would also be a clear signal of the administration’s intention to move more aggressively against Iran. The Trump White House, in far stronger terms than its predecessor, has echoed Saudi and Emirati charges that Iran is training, arming and directing the Shiite Houthis in a proxy war to increase its regional clout against the Gulf’s Sunni monarchies.

The administration is in the midst of a larger review of overall Yemen policy that is not expected to be completed until next month.

But the immediate question, addressed by Mattis’s memo and tentatively slated to come before the principals committee of senior national security aides this week, is whether to provide support for a proposed UAE-led operation to push the Houthis from the port of Hodeida, through which humanitarian aid and rebel supplies pass.

The Pentagon memo does not recommend agreeing to every element of the Emirati request. A proposal to provide American Special Operations forces on the ground on the Red Sea coast “was not part of the request [Mattis] is making,” said a senior administration official, who spoke on the condition of anonymity to discuss planning and the review.

This official and several others said that Mattis and his advisers have asked for removal of President Barack Obama’s prohibitions, which would enable the military to support Emirati operations against the Houthis with surveillance and intelligence, refueling, and operational planning assistance without asking for case-by-case White House approval.

A similar Emirati proposal for help in attacking Hodeida was rejected late last year by the Obama administration, on the grounds that Emirati ships and warplanes, U.S. Special Operations forces and Yemeni government troops were unlikely to succeed in dislodging the entrenched, well-armed rebels and could worsen the humanitarian situation. The effort was seen as sure to escalate a war that the United States and the United Nations have been trying to stop.

Some advisers to President Trump share those same concerns, the senior official said. “There has been no decision yet as to whether [the restrictions] will be lifted. There is certainly broad disagreement across our government.”

While acknowledging that some might see ending the limits as “a green light for direct involvement in a major war. . . . We can’t judge yet what the [review] results will be,” the official said, adding that the limits could be modified, removed or left in place.

Advisers are considering whether direct support for the anti-Houthi coalition would take too many resources away from the counterterrorism fight against al-Qaeda in the Arabian Peninsula and a nascent Islamic State organization in Yemen, the U.S. priority there.

At the same time, what is described as a bare-bones UAE plan has given rise to worry that the Emiratis may not be capable of such a large operation, including holding and stabilizing any reclaimed area, without sucking in U.S. forces.

Without knowing whether the Houthis will give in or fight back — including with Iranian-supplied missiles — there is also concern among U.S. officials that the offensive would further undermine stalemated efforts to negotiate an end to the war and make an already dire humanitarian situation worse.

Yemen’s population centers have been decimated by the conflict, in which indiscriminate Saudi airstrikes and fighting on the ground have killed an estimated 10,000 civilians. Both the Houthis, who hold the capital, Sanaa, Hodeida and other cities, and Saudi Arabia, which controls the sea perimeter around Hodeida, have restricted delivery of aid and other goods flowing through the port to other population centers.

On Wednesday, U.N. humanitarian officials said that millions of Yemenis were on the verge of starvation. Yves Daccord, director general of the International Committee of the Red Cross, warned that an extended battle for the port city would “put even more pressure on the population” and could tip the country into greater humanitarian crisis.

While the warring parties have taken part in U.N.-brokered peace talks, negotiations are stalled and all parties remain in practice most interested in battlefield victory, Daccord said in an interview. “That’s the problem in Yemen,” he said. “They all still think they can win militarily.”

Gulf nations see Hodeida as a vital asset for the Houthis and a lifeline to their backers in Iran.

A plan developed by the U.S. Central Command to assist the operation includes other elements that are not part of Mattis’s request, officials said. While Marine Corps ships have been off the coast of Yemen for about a year, it was not clear what support role they might play.

The Obama administration’s reluctance to take part in the Yemen war was part of Trump’s campaign indictment of his predecessor as “weak” on dealing with Iran, and it led to tensions between the United States and Persian Gulf states.

Obama provided limited support for the Saudi and Emirati operations, selling them weapons and refueling their aircraft. But dismay over reports of Saudi pilots’ repeated strikes on hospitals, schools and other soft targets prompted his administration to distance itself from the Houthi campaign and impose restrictions. Administration lawyers also raised concerns about U.S. legal responsibility for acts committed by the Saudi-led gulf coalition.

Late last year, in response to a particularly gruesome strike, the Obama administration further scaled back support to the air campaign and froze the sale of certain munitions to Riyadh.

For their part, gulf leaders complained that Obama was pushing them to wrap up the war quickly while withholding support they saw as crucial to pushing the Houthis to the negotiating table.

Trump shares the Sunni gulf states’ antipathy for Obama’s Iran nuclear deal, along with their belief that Tehran is the principal driver in the Yemen war, and he has signaled a new approach. In a statement last month condemning Iranian ballistic missile tests, Michael Flynn, then Trump’s national security adviser, spoke at length about the Iran-Houthi threat and said the administration was “putting Iran on notice.”

A senior administration official said at the time that “we assess Iran seeks to leverage this relationship with the Houthis to build a long-term presence in Yemen” and that “we are going to take appropriate action. We are considering a whole range of options.”

Early this month, the State Department approved a resumption of sales of precision-guided munitions to Saudi Arabia. A White House spokesman would not comment on whether Trump had signed off on the sales, saying only that the requisite congressional notification had not yet been made.

For the administration, the response to the Emirati proposal is partly rooted in a desire to act against a troubling threat off Yemen’s western coast, where officials say Houthi missile attacks have endangered freedom of navigation in a key commercial waterway. The Bab el-Mandeb Strait provides a narrow entry into the Red Sea between the Arabian Peninsula and the African continent.

In a rare direct attack on Houthi interests, the United States in October struck Houthi-controlled coastal radar sites with Tomahawk cruise missiles, in retaliation for an assault on U.S. and allied ships. One of the Houthi missiles launched at the USS Mason, a guided-missile destroyer, was fired from Hodeida, officials said at the time.

Restrictions on some intelligence-sharing have already been lifted, allowing the United States to reveal more detailed information on the location of Houthi missile sites. The United States is expected to take other steps to counter that threat, including positioning additional ships in the area.

Some former officials believe stepped-up action is overdue. “One of our bedrock interests in the Middle East is freedom of navigation in and around the Arabian Peninsula, and while I understand why no one wanted to get further enmeshed in the Houthi conflict, we came dangerously close to dropping the ball on protecting our interests toward the end of the administration,” said Andrew Exum, who was a senior Pentagon official under Obama. “We were too hesitant to respond forcefully.”

With Trump’s selection of Mattis to lead the Pentagon and other Iran hawks at the White House, gulf officials see an opportunity to act jointly against their regional rival.

Saudi Maj. Gen. Ahmed Asiri, a spokesman for the gulf coalition, said in a phone interview that “at least now we understand that the government of the United States sees the reality on the ground . . . and that there is a country in the area that wants to use militias and spoil the situation.”

“Now the U.S., Saudis and the UAE are back on the same page,” said Yousef al-Otaiba, the UAE ambassador to Washington. “We’re getting the support we need.”

Full consideration of Mattis’s proposal, and the overall Yemen review, have been delayed by other national security issues, including a major meeting last week in Washington of the 68-member U.S. coalition against the Islamic State.

But if decisions are not made soon, the senior administration official said, “we’re afraid the situation” in Yemen may escalate, “and our partners may take action regardless. And we won’t have visibility, and we won’t be in a position to understand what it does to our counterterrorism operations.”

Regional experts expressed varying opinions about U.S. support for the Hodeida operation,

“My own view is that we should be encouraging the government and the coalition not to undertake offensive actions with the single exception if they can get Hodeida” to relieve the humanitarian crisis, said Gerald Feierstein, a former U.S. ambassador to Yemen.

But April Longley Alley, a senior analyst with the International Crisis Group, warned that the offensive could intensify Yemenis’ suffering and prolong the negotiations stalemate.

“It’s a tragic situation for Yemen, and one that could backfire on the coalition,” Alley said.